Comparison of cardiac and skeletal muscle contraction times: relevance to cardiomyoplasty

A study comparing the timing of myocardial and skeletal muscle contraction is discussed. In 6 normal dogs latissimus dorsi muscle (LDM) contraction times were derived from LDM force and shortening measurements. The LDM was stimulated with a 5 pulse variable frequency pulse train (VFT) and a 6 pulse constant frequency pulse train (CFT). With 6 pulse CFT stimulation, the LDM time to peak shortening and total contraction times were 292.5 ± 27.9 and 456.0 ± 18.8 in the fresh muscle. With 5 pulse VFT stimulation, the LDM time to peak shortening and total contraction times were 242.5 ± 17.6 and 395.5 ± 8.7. Thus, in normal skeletal muscle (i.e., both slow type I fibers and fast type II fibers) contraction times may exceed left ventricular electromechanical contraction times (420 to 294 ms for heart rates from 60 to 120 beats/minute). This prolonged LDM contraction may impede diastolic filling of the left ventricle. Variable frequency stimulation decreases LDM contraction times and thus might prevent this filling impairment